脉冲硬X射线能注量测量技术

阐述了全吸收法测量脉冲硬X射线能注量的基本原理,选择了光电管配合硅酸镥(LSO)闪烁体作为探测系统的核心部件,研制了脉冲硬X射线能注量测量系统.利用该系统测量了"闪光二号"加速器产生的脉冲硬X射线强度,结合灵敏度的实验标定结果,计算得到了脉冲硬X射线的能注量.在连续5发次的实验中,能注量平均测量结果为35.9 mJ/cm2,根据实测剂量和能谱计算得到的能注量为39.8 mJ/cm2,两者的结果比较一致.     

15～600 keV脉冲硬X射线能谱测量

介绍了基于吸收法的脉冲硬X射线能谱测量的基本原理及设计思路,完成了探测器及吸收片的选型,设计了射线准直系统,研究了散射对测量的影响,以12路PIN探测器阵列及铜、铝吸收片为测量核心部件研制了脉冲硬X射线能谱测量系统。实验测量了真空环境下"闪光二号"加速器串级二极管产生的脉冲硬X射线强度,获得了不同衰减程度的实验波形,通过解谱获得了脉冲硬X射线的能谱,光子最高能量约600 keV,平均能量约89.1 keV,与理论计算的结果比较符合。     

整体考虑靶和均整器的设计来提高医用加速器剂量率的方法

通常低能医用加速器靶的设计遵从厚靶原则, 即采用厚度等于或大于电子射程的靶, 使靶后无电子污染. 本文提出了新的靶设计概念：设计靶时, 将靶与相关系统(初级准直锥、均整器)作为一个整体考虑, 通过减小靶厚来提高光子剂量率, 利用初级准直锥、均整器来减少电子污染. 采用这种设计概念, 用蒙特卡罗方法对BJ-6—6MV单光子医用电子直线加速器的靶进行优化设计. 模拟计算10cm×10cm野, 30cm×30cm野的深度剂量曲线, 结果表明：较之现有的厚靶, 治疗剂量提高了10%, 同时表面剂量、X射线的品质仍满足国标的要求. 通过薄靶、厚靶的加速器整机对比实验, 已验证了此结论的正确性.     

光子计数型CCD测量激光等离子体X射线

 介绍了光子计数型电荷耦合器件(CCD)的工作原理，标定了2.0~30 keV的探测效率。在超强超短激光等离子体相互作用中，实验用靶为复合靶，分别用Cu＋Mo和Al+Cu制作。第1层靶是Cu或Al物质作为电子示踪材料，第2层靶是Mo或Cu物质作为荧光材料，利用光子计数型CCD测量了Mo和Cu的X射线能谱, 同时得到CCD的能量分辨率大于37。该CCD可用于激光等离子体低通量高能X射线测量实验。     

聚龙一号丝阵负载Z箍缩硬X射线能谱测量

为获取聚龙一号实验装置负载放电产生硬X射线的能谱分布,设计了一套7通道硬X射线能谱仪。介绍了这套多通道硬X射线能谱仪的测谱原理、主要参数及根据测量结果回推光源辐射能谱的解谱算法。在聚龙一号装置丝阵负载物理实验中对测量系统进行考核,获得了信噪比较高的测量波形。利用最大熵方法进行解谱,获得了丝阵负载产生的硬X射线能谱分布,辐射能段主要集中在200~500 keV附近,且1 MeV以上光子份额较低。     

强激光打固体靶所致硬X射线屏蔽模拟研究

强激光与固体靶相互作用产生的硬X射线已被证实为一种新的电离辐射源,其辐射防护问题引起国内外相关领域的广泛关注。为了便于开展这类电离辐射源的屏蔽设计,研究了强激光打靶所致硬X射线在常用屏蔽材料中的剂量衰减曲线和十值层（TVL）。利用蒙特卡罗程序FLUKA建立了强激光打靶所致硬X射线的屏蔽计算模型,开发了专门的统计程序,解决了屏蔽层之间由于粒子反散射造成的重复统计问题,使得可以通过一次模拟得到不同屏蔽厚度下的光子剂量。计算结果表明:当电子温度为0.5~10 MeV时,X射线在混凝土中的十值层从24 cm到56 cm不等。其中X射线的十值层会随着电子温度的增加而增加,并逐渐趋于饱和。而对于铅屏蔽,除了第一个十值层（TVL1）外,平衡十值层随电子温度的变化较小,在4.7~5.4 cm范围内。另外,当电子温度较高时,探测器到屏蔽体的距离不同会使得TVL1值存在明显的差异。     

高能脉冲X射线能谱测量

给出了高能脉冲X射线能谱测量的基本原理及实验结果.采用Monte-Carlo程序计算了高能光子在能谱仪中每个灵敏单元内的能量沉积,利用能谱仪测量了"强光Ⅰ号"加速器产生的高能脉冲X射线不同衰减程度下的强度,求解得到了具有时间分辨的高能脉冲X射线能谱,时间跨度57ns,时间步长5ns,光子的最高能量3.0MeV,平均能量1.04MeV,能量在0.2—0.9MeV之间的光子数目最多,占46.5%.也利用二极管的电压电流波形理论计算了光子的能谱,并与利用能谱仪测得的能谱进行了比较,两种方法所得结果基本一致.     

强流二极管产生脉冲X射线能谱场稳定性研究

 根据二极管结构及运行参数与出射电子、光子能谱的关系，采用Matlab数据处理软件和蒙特卡罗粒子输运计算方法，建立了二极管阳极靶表面出射光子能谱的计算方法。通过多次对二极管单次脉冲运行参数的比较研究，分析了强流二极管多炮运行参数的波动，对所产生的脉冲X射线能谱场稳定性的影响。计算结果表明：电子能谱的差异随着二极管运行的电参数变化而变化，每炮光子能谱谱型的差异趋于减小。当运行参数波动不大时，能谱场稳定性较好。     

强脉冲超硬Ｘ射线产生技术研究

 分析了利用强流脉冲电子束轫致辐射产生强脉冲超硬X射线的几种主要技术途径的特点，以及提高超硬X射线产额的方法；利用MCNP软件计算了电子能量在0.4～1.4 MeV范围内，超硬X射线产生效率与钽辐射转换靶厚度的关系曲线；介绍了在“强光一号”加速器上开展产生强脉冲超硬X射线实验方法与实验结果，获得了3种强脉冲超硬X射线：脉冲宽度约35 ns，输出窗面积约50 cm²，能量密度为5～7 J/cm²；脉冲宽度约35 ns，输出窗面积约50 cm²，能量密度为12 J/cm²；脉冲宽度约35 ns，输出窗面积约500 cm²，能量密度为1 J/cm²。     

强流二极管产生大面积脉冲X射线参数计算

利用二极管的电压电流波形计算了电子束参数,建立了串级二极管和四路并联二极管阳极靶蒙特卡罗粒子输运计算模型,给出了两种情况下轫致辐射X射线场参数。结果表明:阳极靶厚度增加时,轫致辐射X射线平均能量增大,而能量转换效率先增大,后减小;距离串级二极管和四路并联二极管阳极靶5cm位置处,X射线注量分别为76.50,3.74mJ/cm2;光子平均能量分别为81.13,60.77keV;半径为12cm的圆面上,串级二极管X射线剂量呈马鞍形分布,均匀性为1.70∶1;边长为52cm的正方形平面上,四路并联二极管X射线剂量均匀性小于6.30∶1;电子束轫致辐射转换效率分别为0.29%,0.32%。     

Untersuchung der Polarisationsebene von Photonen nach Compton-Streuung an polarisierten Elektronen

Two polarization phenomena in Compton scattering by polarized electrons were investigated. In the first experiment, the rotation of the polarization plane of photons passing through magnetized iron and gadolinium was measured. This effect arises from a spin dependence of the Compton forward scattering amplitude. For 228 and 333 keV photons and iron absorbers, the observed rotation angles areφ ₀=(3.90±0.57) ×10^?3 rad · cm^?2 and (4.75±0.58)×10^?3 rad · cm^?2, respectively. Secondly, the orientation of the photon polarization plane after scattering of unpolarized photons by polarized electrons was measured. This experiment tests time reversal invariance in quantum electrodynamics. No dependence of the polarization plane on the direction of the electron spin was found within 2×10^?3.     

Monte Carlo calculation of electron spectra produced in water phantoms by 20 keV-1 GeV photons

Abstract

A Monte Carlo calculation for the energy spectra of electrons and positrons produced in infinite and semiinfinite water phantoms by photons ranging in energies from 20 keV to 1 GeV are presented. The dominant processes considered are the photoelectric effect, Auger effect, Compton effect, pair, and triplet production. Bremsstrahlung produced by electrons and positrons with energies greater than 1 MeV is also included. The effect of multiple Compton scattering, not considered in the earlier calculation, for the infinite phantom for photon energies higher than 2 MeV has been incorporated. For a semi-infinite phantom, multiple Compton scattering and backscattering through the top are considered. The results are compared with the earlier calculations for the first-collision spectrum. It is found that the inclusion of multiple Compton scattering significantly increases the average number of electrons/cm³ per photon/cm² at all energies considered whereas bremsstrahlung reduces the number of high energy electrons and produces more low energy electrons in the spectrum.     

一台基于串级二极管技术的高强度脉冲硬X射线源

介绍了利用串级二极管产生高强度脉冲硬X射线的方法及其辐射场参数。以“闪光二号”加速器为平台,通过适应性改造,产生快前沿电压脉冲;研制了两级阻抗1 Ω串级二极管,通过串联分压降低二极管端电压、各级二极管电子束独立打靶在空间叠加形成高强度均匀辐射场。解决了悬浮电极绝缘支撑、二极管阴极均匀发射等技术难题,实现了串级二极管的稳定工作。在总电压约700 kV、电流约310 kA条件下,X射线平均能量87 keV,500 cm2上的平均能注量36 mJ/cm2,剂量均匀性（最大值比最小值）达到2∶1。     

Hard X-ray emission by clusters in an intense femtosecond laser field during collective recombination

We consider the new mechanism of X-ray generation by clusters under irradiation by femtosecond laser pulses, the so-called collective photorecombination. We develop the theory of the photo-recombination of electrons that pass from atomic clusters at the outer ionization to the ground level of a homogeneously charged cluster. Such a cluster is considered to be a quantum potential well. The dipole approximation is inapplicable for this process. We conclude that X-ray photons in collective photorecombination on a charged cluster as a whole have an energy that is much larger than that for photorecombination on separate atomic ions inside the cluster. For a typical cluster of 2.25 × 10⁶ electrons, with a radius R = 300 Å, and a number density of plasma electrons n _e = 2 × 10²² cm^?3, we find that at a 5% outer ionization of this cluster, the energy of hard X-ray photons is 7.2 keV.     

邻苯二钾酸氢铊晶体积分衍射效率的标定

 以北京同步辐射实验室4B7中能束线为光源，在2.1~6.0 keV的范围内对邻苯二钾酸氢铊(TlAP)平面晶体一、二 、三级衍射的积分衍射效率进行了精确的实验标定。标定结果表明：TlAP晶体有较高的峰值衍射率； 其一级衍射的积分衍射效率向低能端有增加的趋势，而在2.6~5.4 keV的范围内大约为1.53×10^-4 rad；随着衍射级次的提高，衍射效率逐渐减小，二级衍射的积分衍射效率约为一级衍射效率的1/4，三级衍射结果比一级衍射下降一个量级。实验所标定的TlAP晶体可用于平晶谱仪对激光等离子体X射线光谱的定量分析。     

Transition radiation of fast electrons as a broadband vacuum-ultraviolet radiation source

The characteristics of a possible radiation source in the vacuum-ultraviolet and soft X-ray range based on the transition radiation of electrons with an energy of about 100 keV are calculated. The possibilities of enhancing the radiation yield in the geometry of the glancing interaction of electrons with a target are analyzed. The possibility of creating a source with a yield on the order of 10^?5 photon/(eV sr) per electron is demonstrated.     

全光汤姆逊散射X光源数值模拟

 使用蒙特卡罗数值模拟程序研究了不同电子束和激光强度下,尾场电子束与超短脉冲激光发生汤姆逊散射获得的X光子能谱、角分布等,初步探索了180°散射下高质量X射线光源所需要的电子束与激光强度。数值模拟结果显示,为了尽量提高光子产额并抑制非线性效应,激光归一化强度应为1的量级。为了获得方向性和单色性好、亮度高的X射线脉冲,需要较高的电子能量和较小的电子能散,电子束脉冲尽量短,且发散角尽量小。     

Determination of experimental K-shell fluorescence yield for potassium and calcium compounds

K-shell fluorescence yields were experimentally determined for potassium and calcium compounds using a Si(Li) X-ray detector system (FWHM=5.96 keV at 160 eV). The samples were excited by 5.96 keV photons produced by a ⁵⁵Fe radioisotope source. The experimental values are systematically lower than the theoretical values.      

Tunable source of parametric X-ray radiation

A new design of an X-ray source with a radiation energy controllably varying from 2 to 130 keV and a radiation intensity exceeding >10^?5 photon/e^?/sr is suggested. The source is based on parametric X-ray radiation (PXR) generated by moderately relativistic electrons in an original geometry. In this geometry, kinematic bunching of PXR reflections is used, which makes it possible to increase the intensity of the source. A model to calculate the PXR characteristics that takes into account absorption of radiation, beam parameters, multiple scattering, and energy loss is developed. The monochromaticity of the source lines is estimated.     

X-ray emission from plasma generated by nanosecond laser irradiating tantalum

A continuum spectrum of X-rays, originating from the interaction of a moderate intensity nanosecond Nd:Yag laser (1064 nm, 9 ns, 30 Hz, 900 mJ, 10¹¹ W/cm²) with metal targets producing plasma, is investigated. The photon emission intensity is particularly high when the plasma expands in a low-pressure gas. The photon energy is measured through selective thin absorber films employed in front of the solid state detector. The temperature of the hot electrons generated from the plasma, responsible for the continuum spectrum emission, is calculated from the fit of the X-ray spectrum with a Maxwellian distribution, and it is about 1–2 keV.